In the aftermath of the attacks of September 11 and the anthrax scare, we have a heightened awareness of US vulnerability to bioterrorism. One of the most feared infectious agents is variola virus, the causative agent of smallpox. The vaccine for smallpox, vaccinia virus (VV), is highly effective, but has an unacceptable rate of complications. Severe illness or death is rare in people with normal immune responses, but considerably more common in individuals with cell-mediated immune defects. The number of individuals that are at risk from this normally innocuous vaccine has greatly increased with the spread of the human immunodeficiency virus (HIV), requiring further improvement in the safety and efficacy of the vaccine. Poxviruses have multiple immune evasion genes that code for proteins that suppress the innate and adaptive immune responses and increase virulence. We have worked extensively to investigate the effects of inactivating VV immunomodulating genes including the interferon-gamma (IFN-gamma) receptor homolog (B8R) and serine protease inhibitors (B13R, and B22R). We have also demonstrated that rVVs expressing IFN-gamma have enhanced safety and efficacy. Based on our past experience, we propose developing a safer and more efficacious rVV based on the Wyeth strain for use as a smallpox vaccine as well as a vector for other infectious disease vaccines. IFN-gamma is a lymphokine that affects both innate and adaptive immune responses. We propose to enhance the safety and efficacy of smallpox vaccine by deleting VV innate immune suppressing genes and co-expressing the IFN-gamma gene. Preliminary safety and efficacy testing of our vaccines will be first determined in a murine model before testing the most promising recombinants in the more expensive nonhuman primate model.